What are Neonicotinoids?

Neonicotinoids (neonics) are a relatively new type of insecticide, used in the last 20 years to control a variety of pests, especially sap-feeding insects, such as aphids on cereals, and root-feeding grubs.

Neonics are systemic pesticides. Unlike contact pesticides, which remain on the surface of the treated foliage, systemics are taken up by the plant and transported to all the tissues (leaves, flowers, roots and stems, as well as pollen and nectar). Products containing neonics can be applied at the root (as seed coating or soil drench) or sprayed onto crop foliage. The insecticide toxin remains active in the plant for many weeks, protecting the crop season-long.

Neonicotinoids in Agriculture

In the UK, five neonicotinoid insecticides are authorised for use in agriculture: acetamiprid; clothianidin; imidacloprid; thiacloprid; and thiamethoxam. They are used as:

seed treatments for cereals and sugar beet (the widest use)

soil treatment for pot plants in the ornamental sector

treatment for turf in the amenity sector

foliar sprays on apples, pears and a range of glasshouse crops

Neonicotinoids, especially seed treatments of imidacloprid, clothianidin and thiamethoxam on arable crops, have become of increasing concern to beekeepers and bee researchers in recent years with many of them suspecting that they may be connected to current bee declines.

Risk to Bees and Other Pollinators

In 2013, the European Union’s pesticide risk assessors revised their conclusions to recognise that use of these three neonics on flowering crops can pose a high risk to bees. Since then, EU countries have implemented a partial ban on imidacloprid, clothianidin and thiamethoxam use, prohibiting most uses on crops attractive to bees. These include oilseed rape, maize, sunflowers, and products sold to the public. Uses in greenhouses, winter sown cereals and as foliar sprays on crops after flowering are still permitted, while there are no restrictions on another two neonics, acetamiprid and thiacloprid.

How do Neonics Work?

Neonics affect the central nervous system of insects. They bind to receptors of the enzyme nicotinic acetylcholine, causing excitation of the nerves, leading to eventual paralysis and death. This specific neural pathway is more abundant in insects than warm-blooded animals, so these insecticides are selectively more toxic to insects than mammals.

Bees have a particular genetic vulnerability to neonics because they have more of these receptors than other insects, as well as more learning and memory genes for their highly evolved system of social communication and organisation, Unlike many insect pest species which are able to detoxify harmful chemicals, bees possess fewer genes for detoxification.

While the older organophosphate and carbamate insecticides tend to degrade quite rapidly in the environment, neonics are more persistent. Imidacloprid can last for months or years in soil and may leach into groundwater under some conditions.

Because they are biologically active at very low concentrations, neonics can be applied at much lower volumes in the field than the older groups of insecticides – in doses of a few grams, rather than kilos, per hectare of the active ingredient.

Neonics were originally welcomed as much safer for humans, livestock and birds than other insecticides. Seed treatments were seen as a more effective method of targeting pests than spraying crop foliage, and more environmentally-friendly because they can reduce the number of spray applications needed in-field. However, over time, it has become clear that they pose different and poorly understood risks to bees and other non-target invertebrates precisely because of the properties that have made them so useful to farmers: their systemic action; their persistence in crops and soil; and their potency at low concentrations. Added to this, their widespread use in many cropping systems and their unplanned presence in pollen and nectar builds up a worrying picture of low level but continued exposure for pollinators, which our regulatory risk assessment schemes are only starting to address.

Why are Neonics so Bad for Bees?

Acutely Toxic by Direct Contact

Like many other broad-spectrum insecticides, neonicotinoids are acutely toxic to bees and other pollinator species by direct contact or by mouth. To prevent accidental contact exposure, products containing neonics carry warnings on the label and instructions to avoid spraying on crops in flower or at times when bees are foraging in fields or close by. Making sure that all farmers comply with these instructions remains a challenge.

Sublethal Effects in Pollen & Nectar

Neonics may be present in pollen and nectar at levels sufficient to impair pollinator health, including disruption to foraging behaviour, homing ability, communication and larval development. Neonic levels in pollen can cause chronic harm to the bee brood. Several studies show that exposure to insecticides at low doses can negatively affect the immune system of bees, making them more susceptible to the impact of parasite and disease infections. A clear increase in growth of Nosema fungal disease was reported in bees reared in colonies exposed to very low doses of imidacloprid, at levels below those considered harmful to bees.

Toxic Breakdown

Neonic breakdown products can be much more toxic than the original pesticides, posing a risk to bee larvae which may be exposed to the longer-lasting breakdown products inside the hive.

Exposure Via Other Routes

Neonics can also remain active in the soil for months, either being taken up unintentionally by crops in the following season or being transported in soil dust to contaminate flowering weeds or contact insects directly. Research also shows that very high concentrations of insecticides can be excreted by treated seedlings in ‘guttation’ droplets on young leaves, posing a risk to bees and other insects which sometimes collect these droplets as drinking water for the hive.

Mechanical Problems with Treated Seeds

There have been numerous serious acute bee poisoning incidents due to mechanical problems with the seed treatment process and field sowing of neonicotinoids. In southwest Germany in 2008, millions of bees died following sowing of maize seed treated with clothianidin. The seed companies involved had failed to apply the sticking agent properly during seed treatment, causing clothianidin-laden dust to be released from the drilling machines. In parts of the US Mid-West in 2010, significant bee kills were reported during spring sowing of maize. Clothianidin and thiamethoxam were found responsible, via the talc used to allow treated seed to flow smoothly through the air-assisted planter equipment. Bees were killed through exposure to the contaminated talc exhaust behind the tractor.

Boom in Neonics

Neonicotinoids are a rapidly growing sector of the pesticide market globally, used on more than 140 crop varieties. They are applied in a wide variety of settings against pests in soil, seed, turf, timber as well as foliar treatments for cereals, cotton, legumes, potatoes, orchard fruits, rice, turf and vegetables. They are also common in veterinary applications such as tick control and flea collars for pets.

The first compound, imidacloprid, was launched by Bayer Cropscience in 1991. Since then a further six compounds have been put on the global market. By 2008 neonicotinoids had taken a 24% share of the total insecticide market of €6.330 billion.

In the UK, the area of land treated with neonics has more than doubled between 2003 and 2013.

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